The present invention generally relates to energy conserving light dimmers. More particularly, this invention relates to dimmers suitable for high intensity discharge (HID) gaseous lamps.
The development of arc discharge lighting, particularly high intensity discharge (HID) gaseous lamps, opened a new era in lighting technology based on the improved efficacy of low pressure sodium, high pressure sodium and metal halide bulbs. HID bulbs, however, require a long time to warm up to achieve full light output. HID bulbs are thus maintained in an xe2x80x9conxe2x80x9d state to avoid the long warm up time at the expense of an increase in the amount of consumed energy.
The increased use of fluorescent lamps in residential service and increasing demand for light level control resulted in the development of household type fluorescent dimming devices, which control the light level but do not efficiently conserve energy. For example, resistive dimmers are variable resistor devices that reduce the power to the light bulb in accordance to the ratio between the resistances. The overall power consumed remains essentially unchanged. Pulse Width Modulation dimmers are used predominantly with fluorescent lighting. These dimmers have a better efficacy than standard dimmers, but such dimming devices are costly for both the replacement components and the installation. Capactive or Inductive phase shifting dimmers incorporate capactive or inductive elements in the circuit to introduce a phase shift in the electrical supply to the light fixture. By selectively switching, for example, capactive, components in and out of a phase shift dimmer circuit, the phase shift and corresponding power factor, of the input voltage to the light fixture are altered. These dimmers are generally referred to as HI/LO dimmers because there is a high, i.e., full power, full illumination, position and a low, i.e., half power, half illumination, position. Variable autotransformers are another means of reducing the voltage to a light fixture by providing different input voltage levels. The different voltage levels are achieved by changing the position of a mechanical slide contacting one of a plurality of taps on the transformer. Variable auto transformers are constructed generally using toroid or linear transformers, which are more expensive than laminated core rectangular power transformers.
The current technology of dimming devices has been developed primarily for light level control and not for efficient energy conservation. Thus, while the use of gaseous discharge devices is energy efficient and the illumination can be adjusted, gaseous discharge devices consume more energy than is necessary. Hence, there is a need for dimming devices that are able to control the level of illumination of gaseous discharge devices and conserve energy in a more efficient manner.
The present invention discloses an apparatus to control the voltage and current levels supplied to a gaseous discharge device to dim the light output and to conserve energy. In accordance with the principles of the invention, a phase detector monitors the phase angle difference between the voltage and current applied to a gaseous discharge device, i.e., load side. When a request to alter the light output level of the discharge device is made, a controller circuit, in response to an indication of the load side voltage/current phase relationship and the requested alteration, causes a change in the supplied voltage and current. When the appropriated phase relationship is determined, the voltage level is altered in a manner such that the alterations occur in a time period, which prevents the extinguishing of the illuminating arc in a gaseous discharge device. Further, the voltage is prevented from falling below a minimum value needed to sustain the illuminating arc in the gaseous discharge device. In another aspect of the invention, the input electrical supply is provided directly to the light circuit to produce a maximum illumination output if a failure is determined to exist in the power dimmer circuit or if the voltage falls below a minimum level.